Usually there is almost no possibility that a motor vehicle supported on wheels support plates of a lift system may drop therefrom, provided that the vehicle has been located correctly in a safe position on the support plates. However, if, for example, one fails to apply the brakes before lifting up a motor vehicle on the support plates, the vehicle may move forward on the support plate and drop from the rear end thereof when the vehicle is being lifted up or when the vehicle is in a lifted position. Conventionally such a danger has been eliminated by placing inverted 'V-shaped wheel stoppers on the support plates, before lifting a motor vehicle up, such that the stoppers engage the wheels of the vehicle. This method of preventing the vehicle dropping from the support plates is troublesome, however, since it is necessary to remove the stoppers from the support plate when the lift system is not used and to place the stoppers in the necessary positions on the support plates which are different with different vehicles. In addition, both the placement of the stoppers on the support plate and the removal of the stoppers therefrom are manual works.